This invention generally relates to data processing systems and more specifically to secondary storage facilities utilized for storing data in such systems.
A secondary storage facility used in a data processing system generally comprises a controller and one or more drives connected to the controller. The drives include direct access memory devices, such as magnetic disk or drum memories, and newer magnetic bubble memories.
These secondary storage facilities, especially facilities using magnetic disk memory devices as the drives, have become very sophisticated in recent years. However, the circuitry that is required in such facilities has increased in complexity. For example, individual drives may include many registers for storing information that is necessary to enable the drives to perform control functions, such as a simultaneous positioning of reading and writing heads in different drives. Both control information (such as sector and track addresses) and data are transferred by producing related signals in parallel. This requires an increase in the amount of hardware associated with each drive since the information recorded on each drive is in serial form.
The cables that interconnect the magnetic drives and their associated controller also comprise large numbers of conductors. This further increases the hardware complexity because each conductor in such a cable requires at least a receiver and/or transmitter for each conductor terminations at both the controller and at each drive. These cables contain so many conductors that they become physically large and stiff. They are therefore unwieldy to handle. As a result, both the labor and hardware costs for installing cables can become a significant portion of the total costs of a secondary storage facility.
As such facilities become more complex, the chances of a malfunction occurring increase. Furthermore, the sheer number of circuits and the use of parallel signal transfers make the diagnosis of such malfunctions more difficult.
Therefore, it is an object of this invention to provide a secondary storage facility, and more specifically a drive for use in such a facility, that improves reliability by reducing circuit complexity.
Another object of this invention is to provide a drive and a secondary storage facility in which the complexity and costs of interconnecting the drive with its controller are reduced over prior facilities.
Still another object of this invention is to provide a drive and a secondary storage facility in which the diagnosis of malfunctions that occur within the facility is simplified.
Yet another object of this invention is to provide a drive and a secondary storage facility in which the overall cost of the drive and the facility are reduced by eliminating redundant hardware, especially in the drives.